Insoluble polyanionic anthraquinones with two strong ionic O-K bonds as stable organic cathodes for pure organic K-ion batteries

Abstract

A new organic cathode namely potassium 2,6-dihydroxyanthraquinone (AQ26OK, theoretical capacity (C^T) = 169 mA h g⁻¹) is synthesized and fully characterized for K-ion batteries. AQ26OK is called polyanionic organic cathode because it has a polyanionic organic skeleton (−2 valent) and two strong ionic K-O bonds. Consequently, the polyanionic AQ26OK is hardly soluble into most organic liquid electrolytes. In half cells (0.3–3.4 V vs. K⁺/K) using 1 mol L⁻¹ KPF⁶ in dimethoxyethane, AQ26OK delivers a highly stable specific capacity of 201 mA h g⁻¹@50 mA g⁻¹ over 450 cycles (4-month test) and realizes ~106 mA h g⁻¹ for 3200 cycles at 500 mA g⁻¹. Using the reduced state (K⁴TP) of potassium terephthalate (K²TP) as the organic anode, the resulting K⁴TP II AQ26OK organic potassium ion batteries can display a highly stable average discharge capacity of 135 mA h g⁻¹_cathode over 250 cycles at 100 mA g⁻¹ and ~47 mA h g⁻¹ for 1000 cycles at 500 mA g⁻¹ during the working voltage of 0.01–3.1 V. To the best of our knowledge, AQ26OK is among the best stable cathodes reported for K ion batteries.

摘要

有机小分子电极材料普遍会溶解在电解液中. 本文报道了一个新型有机小分子化合物蒽醌-2,6-二羟基钾(AQ26OK, 理论比容量:169 mA h g⁻¹)作为钾离子电池的正极材料. AQ26OK在大π共轭蒽醌的基础上含有2个强的O-K离子键, 使得有机框架为−2价. 因此, AQ26OK可以称为多阴离子有机电极材料. AQ26OK在醚类电解液中基本不溶, 从而在钾离子电池中展现出较高的循环稳定性. 在半电池中(0.3–3.4 V), 使用1 mol L⁻¹ KPF⁶ 乙二醇二甲醚作为电解液, AQ26OK在50 mA g⁻¹的小电流下可以达到201 mA h g⁻¹的比容量, 且可以稳定循环超过450圈(寿命至少4个月); 其在大电流(500 mA g⁻¹)下可以达到106 mA h g⁻¹的比容量且循环3200圈. 在使用对苯二甲酸钾还原态(K⁴TP)作为有机负极的全有机钾离子电池中, 此K⁴TP IIAQ26OK有机钾离子电池(0.01–3.0 V)在小电流(100 mA g⁻¹)下可以稳定循环超过250圈且平均放电比容量约为135 mA h g⁻¹; 其在大电流(500 mA g⁻¹)下循环1000圈的平均比容量约为47 mA h g⁻¹. AQ26OK是目前钾离子电池有机正极中最稳定的材料之一.